This disclosure is directed to a remote control core sample cutting apparatus which particularly includes a closed and sealed cylinder having an internal chamber for receiving a core sample after cutting which is maintained at prevailing downhole pressures receive and store the sample at that pressure. It particularly enables the sample to be retrieved with connate fluids in the core sample.
This feature finds its use especially with a core testing apparatus which forms a core, the improvement relating to the core storage cylinder. In a typical situation, a well has been partially, perhaps even completely drilled and is in the open hole condition. Formations of interest have been identified based on other testing procedures, but the well completion process is materially aided and assisted by furnishing a core sample which is soon analyzed at the surface. A testing tool which cuts a core sample is thus lowered into the open borehole and a core sample is taken. After the core sample has been retrieved to the surface, it is then tested to obtain additional information regarding the nature of the formation and whether or not selected completion procedures need to be implemented for that formation. At least two changes occur on removal of the core sample from the well borehole. These changes degrade the core sample, and may well mislead the analyst who reviews the data obtained from the core sample during surface testing. Among other changes, the core sample is removed from the ambient temperature and pressure which prevailed at the formation of interest. The temperature and pressure change occurs during removal of the testing tool from the borehole, potentially enabling oil, gas, water or other fluids captured in the pores of the sample to escape. This leads to an unwanted detrimental result, namely that connate fluids from the formation potentially escape from the core sample and are lost. For instance, if the formation of interest is sufficiently pressured certain light hydrocarbons may exist as light liquids and may boil off in the gaseous state and evaporate when exposed to a reduced temperature and pressure. At least, certain light molecules will escape. Any analytical data thereafter obtained from the core sample will be in error, at least to the extent of loss of connate fluids as gas.
This apparatus incorporates a closed and sealed cylinder which has an internal chamber. After the core sample has been cut, the cylinder is opened while the tool is at the requisite depth, the sample is thereafter retrieved from the formation and inserted into the cylinder. The cylinder is selectively opened and closed to capture the core sample. Moreover, fluids in the core sample are maintained at the prevailing pressures and temperatures until they are enclosed in the cylinder. After sealing, the connate fluids along with the core sample are not permitted to escape and the retrieved sample more nearly represents prevailing conditions at the formation of interest.
The present apparatus thus discloses a sample cutting tool in a sonde adapted for lowering in a borehole on a logging cable. The sonde supports a mechanism operating the core holder to extend into the formation, cut a core, capture the core within the holder and retrieve the core sample from the formation back into the sonde. A removable cylinder is loaded into the sonde at the surface. The cylinder is aligned so that it has an opening through which the core holder can be inserted. A core punch is extended to drive the core sample from the core holder and it is forced into the cylinder. The cylinder has appropriate valves and seals to limit entry so that it can be opened and closed to timely receive the core sample. The removable cylinder is preferably operated with a pressure balance system so that cylinder internal pressure equals the pressure at the formation of interest. The cylinder has other fittings and valves enabling connections to be made to the cylinder after retrieval from the surface The fittings and valves enable controlled pressurization of the interior of the cylinder which thereby regulates the pressure on the sample. Appropriate tests can be run on the sample at the surface while maintaining the sealed system around the core sample. Such tests include measuring saturation of the core sample with connate fluids including gases, oil, and water. Electrical induction tests can also be run in the cylinder. The disclosure sets forth the cooperative surface equipment which is releasably connected to the cylinder to accomplish these tasks.